Electroexplosive cartridge with heat sink button



1965 s. A- MOSES ET AL 3,227,083

ELECTROEXPLOSIVE CARTRIDGE WITH HEAT SINK BUTTON Filed Jan. 30, 1964 INVENTOR. S/D/VEY A. MOSES BY JOHN W HASSLER ATTORNEYS United States Patent 3,227,083 ELECTROEXPLOSIVE CARTRIDGE WITH HEAT SlNK BUTTON Sidney A. Moses and John W. Hassler, Hollister, Calif., assignors to Holex Incorporated, Hollister, Calif., a

corporation of California Filed Jan. 30, 1964, Ser. No. 341,247 '7 Claims. (Cl. 102-28) This invention relates to improvements in electroexplosive cartridges, and particularly to improved electroexplosive cartridges that are better protected from accidental firing.

The current or power which actuates an electroexplosive cartridge is introduced into the interior of the cartridge through lead-in pins, which are fused in glass or bonded inplastic. A high-resistance wire, known as a bridge wire, is welded to the interior ends of the lead-in pins. When the firing current passes through the bridge wire, it heats the bridge wire, and this heat is used to raise the temperature of the explosive prime. When the prime has been heated to its activation temperature, it explodes and fires the cartridge.

The trouble has been that the cartridges are often used in environments where they are subject to conditions that accidentally send current through the bridge wire. Sometimes the cartridges are in electromagnetic fields where currents are induced in the lead-in pins; sometimes the cartridges are exposed to electromagnetic radiation. Cartridges which ordinarily are quite safe may become very dangerous in such environments, for sometimes the current sent accidentally through the bridge wire has been sufiicient to heat the prime t its critical temperature, causing it and the cartridge to explode.

Accordingly, the present invention relates to the problem of protecting electroexplosive cartridges from accidental firings and to enable them to pass substantial amounts of current for a substantial length of time through the bridge wire without causing accidental firing, while at the same time maintaining the ability of the cartridge to be ex loded instantly and at will when firing is desired.

Other objects and advantages of the invention will appear from the following description of a preferred embodiment thereof.

In the drawings:

FIG. 1 is an enlarged view in perspective and in section of an electroexplosive cartridge embodying the principles of the present invention, shown before installation of the explosive prime and a protective button.

FIG. 2 is a view in elevation and in section of the cartridge of FIG. 1 showing the button and the prime in place.

FIG. 3 is a view in section taken along the line 3-3 in FIG. 2.

The cartridge 19 shown in the drawings includes a metal housing 11 having an interior well 12 with a tapered portion 13, in which a plastic or glass plug 14 is fused. Typically, the housing 11 has a hexagonal collar 15 between upper and lower externally threaded portion 16 and 17 for attaching it where desiredone or more pairs of lead pins 18 and 19 extend through the plug 14 and are connected together electrically by a bridge wire 2%). A single bridge wire 2%) may connect a single pair of lead pins 18 and 19, but duplication is more normal, so that there are two bridge wires 21), one for each pair of lead pins 18 and 19, in order to increase the probability that the cartridge 10 will fire when it is supposed to, regardless of malfunctions that tend to occur. The cup 11 contains an explosive prime charge 26, such as mixture of Zirconium and ammonium perchlorate, which will not explode until a temperature of at least 500 F. is reached.

In the present invention, a heat-sink cup 21 is provided in the housing 11, resting on the upper end of the plug 14. The cup 21 has a central portion 22 with an upper surface 23 on which the bridge wires 20 rest, and has a rim or wall 24 extending up around the periphery, in contact with the inner surface 12 of the housing 11. The cup 21 is an effective heat sink, and an additional heat sink barrier 25, preferably in the form of a loose button, is sealed in the cup 21, in direct contact with the surface 23, the bridge wires 20, and the wall 24. The prime 26 is placed above the button 25, which shields most of the explosive electrically-conductive prime 26 from direct contact with the bridge wires 29. For each bridge wire 20, the heatsink button 25 has two holes 27, 28, and the button 25 is oriented so that each hole 27, 28 overlies one end of the bridge wire 20. Each hole 27, 28 is filled with prime 26, and these little hole-filling portions are the only parts of the prime 20 in actual contact with either bridge wire 20.

Without the heat-sink button 25, the hottest part of the bridge wire 29 would be at its midpoint, and the coolest parts would be its ends where the bridge wires 29 are connected to the lead pins 18, 19, as by welded contacts 30, 31. In this invention the central portion of each bridge wire 24 is sandwiched between the heat sink material of the cup 21 and the heat sink button 25, so that there is only limited contact between the bridge wires 20 and the prime 26 and so that the exposed portions of the two welded contacts 39, 31, which now become the hottest spots along the wire 29, are used as the activating portion thereof. The heat sink sandwich 22, 25 keeps the other parts of the bridge wire 20 cool.

The cartridge 10 is completed by covering the prime 26 with a barrier or cover 32 (preferably of plastic, such as polyethylene, or paper, or other dielectric material), preferably across the top of the cup 21, and then packing the main ignitable explosive charge 33 over the cover 32 in the housing 11. Usually the explosive charge 33 is a poor conductor of electricity.

To understand the invention, two related, but separate, factors should be considered: (1) the quantity of heat generated by a bridge Wire by the current passing through it, and (2) the maximum temperature created by this heat at the interface between the bridge wire and the explosive.

(1) Basically, the heat is given by the well-known equatron:

Q=0.241 I Rt, Where:

Q is the amount of heat in calories,

I is the current in amperes R is the resistance in ohms of the bridge wire, and

t the time in seconds during which the current I is passed.

Thus, with 1 ampere of current passed through a 1- ohm bridge wire for five minutes, 72.3 calories of heat are released. (Q=0.241 1 1 1 5 60=72.3). However, not all this heat acts to heat the prime 26; the heat is dissipated not only in heating the prime 26, but also in heating the bridge wires 20, in heating the various components of the cartridge 10, including the heat-sink cup 21 and the heat-sink button 25, and in heating the air or other material surrounding the cartridge 10.

(2) The temperature to which each bridge wire 20 is raised is a complicated function of many factors, including the value of the applied current, the time during which the current flows, the resistivity of the bridge wire material, the diameter of the bridge wire, the emissivity of the bridge wire, the specific heat of the bridge wire, the thermal conductivity of the bridge wire, and the density of the bridge wire. However, it is also a function of the following factors: the specific heat, thermal conductivity,

density, mass, and ambient temperature of the material surrounding the bridge wire.

In this invention, the cup 21 and button 25 surround the bridge wires 20, and both the cup 21 and the button 25 are preferably made from beryllium oxide (BeO) or aluminum oxide (A1 or other similar ceramic or ceramic-coated material. Therefore, they dissipate a large amount of heat and can delay explosion for a long time, so that if extraneous induced currents or electromagnetic radiation act on the cartridge for only a short time, there will be no accidental firing. However, when current is purposely applied to the leads 18, 19 in the large amounts used, the cartridge 1t) fires promptly. There are now two hot spots for each bridge wireat the button holes 27 and 2S-so that reliability of initiation is increased when the all-fire current is applied.

The heat sink sandwich 21, 25 keeps the bridge wires 26 from reaching as high a temperature as they would otherwise reach for any given amperage and the end contact portions become the hottest parts of the wires, though they themselves are cooler than they would otherwise be. Therefore, a higher current can be applied to the leads 18, 19 without firing the prime 26.

To those skilled in the art to which this invention relates, many changes in construction and widely ditfering embodiments and applications of the invention will suggest themselves without departing from the spirit and scope of the invention. The disclosures and the description herein are purely illustrative and are not intended to be in any sense limiting.

We claim:

1. An electroexplosive cartridge, comprising a heat-sink cup having a depressed central surface,

lead wires passing through said cup,

a bridge wire lying on said cup surface and connecting two lead wires,

a heat sink button overlying said bridge wire and filling the bottom of said cup and having a through opening overlying each end of said bridge wire, said button being otherwise imperforate, and

an explosive prime charge filling said cup above said button and filling said through openings.

2. An electroexplosive cartridge, comprising a cup of heat sink material having a flat central surface surrounded by Walls of heat sink material,

lead wires passing through the bottom of said cup to said surface,

a bridge wire lying on said central surface and connecting two lead wires,

a button of heat sink material overlying said bridge wire and occupying the portion of said cup immediately above said surface and having a through opening overlying each end of said bridge wire, said button being otherwise imperforate, and an explosive prime charge filling said cup above said button and said through openings. 3. The cartridge of claim 2 wherein said heat sink material is, in both instances, beryllium oxide.

4. The cartridge of claim 2 wherein said heat sink material is, in both instances, aluminum oxide.

5. The cartridge of claim 2 wherein said heat sink button and cup have a ceramic surface.

6. An el ctroexplosive cartridge, comprising a tubular metal housing,

a fused insulating plug in said housing,

a cup-shaped member in said housing resting on said plug with side walls extending away from said plug and a central portion of .said cup,

lead wires passing through said plug and said cup to the upper surface of said outer portion,

a bridge wire lying on said surface and connecting two lead wires,

a button sealed in said cup directly overlying said surface and said bridge wire and filling the bottom portion of said cup and having a through opening in line with each end of said bridge wire, said button being otherwise imperforate, and

an explosive prime charge filling said cup above said button and said through openings, and

an ignitable charge packed on said prime in said tube.

7. An electroexplosive cartridge, comprising a housing having a plug therein,

a heat-sink cup resting on said plug,

lead wires passing through said plug and cup,

a heat sink button in said cup resting on the bottom thereof overlying said bridge wire,

a bridge wire sandwiched between said cup and said button, and connecting two lead wires,

said button having a through opening overlying each end of said bridge Wire, and

an explosive prime charge filling said through openings and said cup above said button.

References Cited by the Examiner UNITED STATES PATENTS 2,830,671 4/1959 Lutz et a1 10228 BENJAMIN A. BORCHELT, Primary Examiner.

R. V. LOTTMANN, Assistant Examiner. 

1. AN ELECTROEXPLOSIVE CARTRIDGE, COMPRISING A HEAT-SINK CUP HAVING A DEPRESSED CENTRAL SURFACE, LEAD WIRES PASSING THROUGH SAID CUP, A BRIDGE WIRE LYING ON SAID CUP SURFACE AND CONNECTING TWO LEAD WIRES, A HEAT SINK BUTTON OVERLYING SAID BRIDGE WIRE AND FILLING THE BOTTOM OF SIAD CUP AND HAVING A THROUGH OPENING OVERLYING EACH END OF SIAD BRIDGE WIRE, SAID BUTTON BEING OTHERWISE IMPERFORATED, AND AN EXPLOSIVE PRIME CHARGE FILLING SAID CUP ABOVE SAID BUTTON AND FILLING SAID THROUGH OPENINGS. 